Objective To investigate the effects of ketamine on learning and memory function and expression of early growth responsive gene-1 (Egr-1) in hippocampus of minor rats. Methods Twenty minor SD rats were randomly divided into normal saline control group (Ns group) and ketamine group (Ket group). Rats in Ket group were intraperitoneally injected with 50 mg/kg ketamine, and those in Ns group were administrated with same amount of normal saline for 6 d. Morris water maze test was adopted to explore the learning and memory function at 24 h after the final injection. The sections of hippocampus were obtained at 1 h of the final Morris water maze test, and the expression of Egr-1 mRNA and protein was determined by Real-Time PCR and Western blotting respectively. Results In Morris water maze test, the latency in place navigation in Ket group was significantly longer than that in Ns group (P<0.05), and the times of crossing the platform and total swimming distance in Ket group were significantly decreased compared with Ns group (P<0.05). It was revealed that the expression of Egr-1 mRNA and protein in Ket group was significantly lower than that in Ns group (P<0.05). Conclusion Application of ketamine in minor rats may result in learning and memory impairment, and the

mechanism may be associated with the down-regulation of expression of Egr-1 in hippocampus.